Method of forming fine pattern

ABSTRACT

A method of forming a fine pattern according to an embodiment includes: forming a hard mask on a substrate; forming a mask reinforcing member on the hard mask; forming a di-block copolymer layer on the mask reinforcing member, the di-block copolymer layer comprising a sea-island structure; forming a pattern comprising a concave-convex structure in the di-block copolymer layer, with island portions of the sea-island structure being convex portions; and transferring the pattern onto the hard mask by performing etching on the mask reinforcing member and the hard mask, with a mask being the pattern formed in the di-block copolymer layer. The mask reinforcing member is comprised of a material having an etching speed that is higher than an etching speed for the hard mask and is lower than an etching speed for sea portions of the sea-island structure of the di-block copolymer layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2010-208122 filed on Sep. 16, 2010in Japan, the entire contents of which are incorporated herein byreference.

FIELD

Embodiments described herein relate to a method of forming a finepattern.

BACKGROUND

The advancement of the microfabrication technique used for manufacturingsemiconductor devices and the like accounts for a large proportion ofthe recent significant improvement in the functions of informationdevices such as personal computers. Conventionally, size reductions inprocessing operations have been achieved by reducing the wavelengths ofexposure light sources used in lithography. However, as the sizes inprocessing operations have become smaller and higher-density patternsare being used, the lithographical processing costs in the manufacturingprocedures are rapidly becoming higher. In the next-generationsemiconductor devices or high-density recording media such as patternedmedia subjected to a microfabrication technique, the pattern sizes arerequired to be reduced to several tens of nanometers or smaller.Therefore, electron beams are used as exposure light sources, but thereremains a serious problem in terms of the throughput of fabrication.

In the above described circumstances, attention is currently focused ontechniques utilizing a phenomenon in which a material forms a certainordered array pattern in a self-organized manner, as the techniques areregarded as inexpensive fabrication techniques that can realize highthroughputs. Particularly, great attention is focused on a techniqueutilizing “block polymers”.

According to a microfabrication technique using a pattern formed byself-organization of a di-block copolymer as an etching mask, sideetching is caused in the etching mask due to the difference in etchingspeed between the mask of the di-block copolymer and the hard mask. As aresult, the shape roughness (the variation coefficient) of the patterntransferred onto the hard mask becomes higher than the shape roughnessof the etching mask.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a) through 1(e) are cross-sectional views for explaining amethod of forming a fine pattern according to an embodiment;

FIGS. 2( a) through 2(c) are diagrams for explaining patterns to beformed by a method according to Example 1 and a method according to acomparative example;

FIG. 3 is a graph showing the relationship between the film thickness ofa mask reinforcing member and the pattern variation coefficient;

FIG. 4 is a graph showing the relationship between the film thickness ofthe mask reinforcing member and the concavities and convexities formedafter the processing of the hard mask;

FIGS. 5( a) through 5(d) are cross-sectional views for explaining amethod of forming a perpendicular magnetic recording medium according toExample 6;

FIGS. 6( a) through 6(c) are cross-sectional views for explaining amethod of forming a fine pattern according to Example 6;

FIGS. 7( a) through 7(d) are cross-sectional views for explaining amethod of forming a fine pattern according to Example 7;

FIGS. 8( a) through 8(c) are cross-sectional views for explaining amethod of forming a fine pattern according to Example 7; and

FIGS. 9( a) through 9(e) are cross-sectional views for explaining amethod of forming a fine pattern according to Example 8.

DETAILED DESCRIPTION

A method of forming a fine pattern according to an embodiment includes:forming a hard mask on a; forming a mask reinforcing member on the hardmask; forming a di-block copolymer layer on the mask reinforcing member,the di-block copolymer layer comprising a sea-island structure; forminga pattern comprising a concave-convex structure in the di-blockcopolymer layer, with island portions of the sea-island structure beingconvex portions; and transferring the pattern onto the hard mask byperforming etching on the mask reinforcing member and the hard mask,with a mask being the pattern formed in the di-block copolymer layer.The mask reinforcing member is comprised of a material having an etchingspeed that is higher than an etching speed for the hard mask and islower than an etching speed for sea portions of the sea-island structureof the di-block copolymer layer.

Embodiment

Before the method of forming a fine pattern according to this embodimentis explained, the outline of this embodiment is described. The inventorsof the invention found that, by inserting an appropriate maskreinforcing member between a hard mask onto which a pattern was to betransferred and a di-block copolymer layer having an array structure,the variation in shape roughness was made smaller when a pattern wastransferred onto the hard mask. By using this technique, the patternformed in the mask reinforcing member can be transferred onto the hardmask, and the pattern transferred onto the hard mask can not be affectedby the polymer subjected to side etching.

Here, the appropriate mask reinforcing member has an etching speed thatfalls between the etching speed for the hard mask and the etching speedfor the later described polymer phases X, and is almost the same as theetching speed for the later described polymer phases Y. By using such amaterial as the mask reinforcing member, the shape of the pattern formedby a di-block copolymer can be accurately transferred onto the hardmask. An “accurate transfer” herein indicates that the shape variationcoefficient is 10% or lower in a pattern transfer from a mask formed bya di-block copolymer onto the hard mask.

The method of forming a fine pattern according to this embodiment isdescribed in detail with reference to the accompanying drawings.

FIGS. 1( a) through 1(e) show the procedures for forming a fine patternaccording to this embodiment. First, a substrate 2 is prepared, and ahard mask 4 onto which a pattern is to be transferred is formed on thesubstrate 2 (FIG. 1( a)). A glass substrate, a sapphire substrate, asilicon substrate, or a substrate having a HDD (hard disk drive)magnetic layer formed thereon can be used as the substrate 2. Thematerial used for the magnetic layer can be an alloy containing Co—Cr orCo—Pt, an alloy containing Fe—Pt, Co—Pt, or Fe—Pd, or a multilayer filmmaterial such as a Co/Pt or Co/Pd film. Having high magnetic crystallineanisotropy energy, each of those alloys and multilayer film materialshas a high resistance to thermal fluctuations. Therefore, using thosealloys and multilayer film materials is preferable. To improve magneticproperties, an additional element such as Ta, Cu, B, or Cr is added tothe alloy or multilayer film material, as needed. As for the magneticlayer, it is more preferable to use CoCrPt, CoCrPtB, CoCrPtTa, CoCrPtNd,CoCrPtCu, FePtCu, or the like. The magnetic layer can be a multilayerstructure that has two or more layers, as needed. In that case, at leastone of the layers should be the above described layer. As for the hardmask, carbon, carbon nitride, silicon, silicon oxide, or the like can beused. Alternatively, a multilayer mask having a structure in which thosematerials are stacked can be used.

A mask reinforcing member 6 is then formed on the hard mask 4 (FIG. 1(b)). The material of the mask reinforcing member 6 will be describedlater in detail. A block polymer layer 8 is then formed on the maskreinforcing member 6 (FIG. 1( c)). The block copolymer used here can bea “di-block copolymer” of an A-B type having the two types of polymerchains, a polymer chain A and a polymer chain B, combined with eachother, for example. A di-block copolymer is a copolymer having twopolymers combined with each other. When annealing is performed at anappropriate temperature, the di-block copolymer is phase-separated intopolymer phases A (hereinafter also referred to as the polymer phase X)and polymer phases B (hereinafter also referred to as the polymer phasesY), to form an ordered array structure. For example, a sea-islandstructure is formed, with the polymer phases X forming the sea, thepolymer phases Y being two-dimensionally arranged as islands in the seaof the polymer phases X. The shapes and sizes of the polymer phases Xand the polymer phases Y forming the ordered array structure depend onthe lengths of the polymer chains A and B. Adjusting those lengths canform minute islands whose diameter is from 100 nm to 10 nm or less.

As a di-block copolymer ordered array structure as described above,there have been a known island structure in which A phases or B phaseshave spherical shapes and are distributed, a cylinder structure in whichA phases or B phases have cylindrical shapes and are distributed, andthe like. An arrangement of those phases can be hexagonal orquadrangular, with the spheres or cylinders being closely arranged. Theordered array structure can have a concave-convex structure havingconcavities and convexities arranged in an orderly manner, but can be aflat structure without any concavities and convexities. In thisembodiment, the di-block copolymer phase-separated structure needs to betransformed into a concave-convex structure. If the surface of the blockcopolymer ordered array structure has concavities and convexities, theconcavities and convexities can be used as they are.

If the block copolymer ordered array structure has a flat structurewithout any concavities and convexities, at least one polymer phase typeof block copolymer needs to be selectively removed. In this embodiment,etching is selectively performed on the polymer phases X forming the seaof the sea-island structure, to form a fine pattern in which the spheresof the polymer phases Y are exposed and are orderly arranged.

A fine pattern structure formed by a block copolymer can be a spherestructure in which the polymer phases X form the sea, the polymer phasesY have spherical island structures, and the spheres are orderlyarranged, or can be a cylinder structure in which the polymer phases Xform the sea, and the polymer phases Y have cylindrical structures. Thedifferences between those structures can be controlled by changing themolecular weights of the polymer chain A and the polymer chain B,surface energy of the substrate, or annealing conditions.

To selectively remove the polymer phases X, a block copolymer should beformed by two or more kinds of polymer chains having differentresistances to energy beams such as plasma beams, light beams, orelectron beams, or heat when any of those beams or heat is applied. Forexample, where N represents the total number of atoms per monomer, Ncrepresents the number of carbon atoms per monomer, and No represents thenumber of oxygen atoms per monomer, the polymer chain having the smallervalue of N/(Nc−No) per monomer has the higher resistance to plasmaexposure. In view of this, two or more kinds of polymer chains havingdifferent plasma resistances from each other can be combined.

Also, it is possible to combine a polymer that has a cross-linkingreaction and becomes hardened when exposed to the plasma beams, lightbeams, electron beams, heat, or the like, and a polymer that does notreact to any of those beams or heat or the like. Further, withaffinities being taken into consideration, a hydrophilic polymer and ahydrophobic polymer can be used, and a cross-linking agent can besegregated in one of the polymers.

As described above, if the block copolymer layer 8 originally has aconcave-convex structure, the concave-convex structure is used as it is,and if the block copolymer layer 8 is flat, concavities and convexitiesare formed in the block copolymer layer 8. In this embodiment, RIE(Reactive Ion Etching) using O₂ is performed on the block copolymerlayer 8, to form a concave-convex structure as a sea-island structurehaving portions 8 b formed by the polymer phases Y and portions 8 aformed by the polymer phases X, with the island portions 8 b being theconvex portions, as shown in FIG. 1(d). Here, part of the portions 8 aformed by the polymer phases X can remain in the concave portions, orthe sides of the portions 8 a formed by the polymer phases X locatedimmediately below the island portions 8 b can be partially removed byetching. As the block copolymer layer 8 having the concave-convexstructure serves as a mask, etching is also performed on the maskreinforcing member 6.

Etching is then performed on the hard mask 4, using a mask patternformed by the block copolymer layer 8 having the concave-convexstructure and the etched mask reinforcing member 6, as shown in FIG. 1(e). In this manner, the pattern is transferred onto the hard mask 4.

In this embodiment, the mask reinforcing member 6 is made of a materialthat is etched by the same etching gas as an etching gas used for thedi-block copolymer, or is made of a material that is etched by oxygen.Also, the mask reinforcing member 6 is made of a material for which theetching speed is lower than the etching speed for the polymer phases Xforming the sea portions of the di-block copolymer layer but is higherthan the etching speed for the hard mask 4, or is made of a material forwhich the etching speed is almost the same as the etching speed for thepolymer phases Y.

A specific example of a material used for the mask reinforcing member 6is an organic polymer chain. With the above described value of N/(Nc−No)being used as a parameter, a relational expression indicating thatV_(etch) is proportional to N/(Nc−No) is established between the etchingspeed V_(etch) of the organic polymer chain and the parameter.Therefore, the material for which an etching speed falls between theetching speed for the sea portions of the sea-island structure and theetching speed for the hard mask 4 can be selected as the maskreinforcing member. For example, in a case where a di-block copolymerhaving PS (polystyrene) and PDMS (polydimethylsiloxane) combined witheach other is used as the block copolymer layer 8, and carbon is used asthe hard mask 4, PVN (polyvinylnaphthalene), PHS (polyhydrostyrene), PVB(polyvinylbiphenyl), PS, or PDMS should be used, with an etching speedfor PS forming the sea portions of the sea-island structure and anetching speed for the carbon being taken into consideration.Particularly, in a case where PDMS is used, the etching speed fallsbetween the etching speed for PS forming the sea portions of thesea-island structure and the etching speed for the carbon of the hardmask 4. Further, since PDMS is the same material as the material of thepolymer phases Y of the island portions of the sea-island structureforming the pattern, the pattern can be more accurately transferred.

In this embodiment, the film of the mask reinforcing member 6 can beformed by either a wet process involving spin coating with the use of aliquid solution or a dry process involving vapor deposition, sputtering,or the like.

A film thickness t_(m) of the mask reinforcing member 6 preferablysatisfies 0<t_(m)<d, where d represents a diameter of each of the islandportions forming the di-block copolymer layer 8. If d is equal to orsmaller than t_(m), etching is performed also on the di-block copolymerlayer 8 when etching is performed on the mask reinforcing member 6, anda roughness of the di-block copolymer layer 8 becomes higher. In extremecases where the roughness of the di-block copolymer layer 8 is greater,the pattern cannot be transferred onto the hard mask 4. If t_(m) is 0,on the other hand, an effect to reduce a shape-roughness cannot beobserved.

Particularly, in the range satisfying 0<t_(m)<d/2, heights of theconcavities and convexities of the hard mask 4 formed by the etching canbe made greater, and a high-aspect pattern can be formed on thesubstrate 2 when processing is performed on the substrate 2 with the useof the hard mask 4. Therefore, it is notable to satisfy 0<t_(m)<d/2.

The di-block copolymer layer 8 can be formed by a spin coatingtechnique, or can be formed by a dip coating technique by which thesubstrate 2 is dipped in a liquid solution and is pulled out of thesolution at a constant speed.

A film thickness t_(d) of the di-block copolymer layer 8 can be changedwith a pitch p of the pattern to be formed. In a case where a mask withexcellent arrangement and dot shapes is to be formed, the film thicknesst_(d) of the di-block copolymer layer 8 satisfies 0<t_(d)<1.5p. If thethickness t_(d) only satisfies 0<t_(d)<p, the dots are not closelyarranged, and missing portions appear in the pattern. Also, the dotshave various sizes. However, the pattern does not cause any problem withthe functions as a mask for microfabrication. If the film thicknesst_(d) is equal to or greater than 1.5p, on the other hand, dot patternis not a single layer, but has a structure in which two or more layersare stacked. As a result, the dot pattern does not function as a mask.If the film thickness t_(d) is about 1.3p, dot arrangement becomestwo-dimensionally hexagonal. The film thickness of each di-blockcopolymer layer 8 in the later described examples is controlled to be1.3p.

In a case where a shape of the pattern varies with film thickness asdescribed above, it is necessary to appropriately adjust the filmthickness in accordance with materials. The film thickness can becontrolled by changing density of solution of the di-block copolymer, orby adjusting the number of rotations and the rotation time in spincoating. Also, the film thickness can be measured with the use of an AFM(atomic force microscope) or a contact level detector or the like.

The di-block copolymer applied onto the substrate is subjected toannealing, to have an ordered array structure. To prevent polymeroxidation, the annealing atmosphere for the di-block copolymer should bea vacuum or a nitrogen atmosphere. Alternatively, the annealing can beperformed in an atmosphere of a forming gas that is a mixed gas ofhydrogen and nitrogen. An annealing temperature can be roughly estimatedby carrying out differential scanning calorimetry (DSC). By performingheating at 5° C./min. and obtaining a DSC chart, information about theglass-transition (Tg) temperature, phase transitions, phasedecomposition, and the like can be obtained. In a case where theorder-disorder transition (ODT) temperature at which the di-blockcopolymer has a phase transition is higher than the temperature ofpolymer decomposition, the annealing temperature should be raised to atemperature immediately below the temperature at which polymers aredecomposed. If the ODT temperature is equal to or lower than thetemperature of polymer decomposition, the annealing should be performedat almost the same temperature as the ODT temperature.

Since the Tg temperature, the ODT temperature, and the decompositiontemperature vary with the types of di-block copolymers, annealing needsto be appropriately performed at an optimum temperature.

The dry etching used for the pattern formation in the di-block copolymerlayer 8 and the pattern transfer onto the hard mask 4 is RIE.Alternatively, the dry etching can be reactive ion beam etching, ionetching, etching using neutrons, or the like.

Examples of RIE include capacitively-coupled RIE, inductively-coupledRIE, and ECR-RIE. However, the same results can be achieved byperforming etching with the use of any device.

In this embodiment, the RIE for the pattern formation in the di-blockcopolymer layer 8 through the RIE for the pattern transfer onto the hardmask 4 are performed in the same gas. Specifically, RIE is performed for30 seconds, where the oxygen flow rate is 20 sccm, the total pressure is0.1 Pa, the input coil power is 100 W, and the platen power is 10 W. Inthis manner, the pattern in the di-block copolymer layer 8 istransferred onto the hard mask 4.

A gas used in the RIE should be oxygen. However, in a case where a smallamount of argon, nitrogen, or fluorine is mixed with oxygen, or where amixed gas that causes a 10% or smaller change in the etching speed forthe di-block copolymer compared with an etching speed for oxygen isused, the etching can also be defined as etching with the use of oxygen,since an etching effect by oxygen is notable in either case.

Pattern shape is evaluated with the use of a variation coefficient (avalue that is obtained by normalizing the standard deviation of thediameters of the dots in the pattern with the mean value of thediameters of the dots in the pattern, and is expressed in percentage). Asmall value is notable as the value of the variation coefficient. In acase where a fine pattern is applied to a patterned medium, the finepattern is required to have the variation coefficient of 10% or lower,according to academic institutes and societies. The variationcoefficient is calculated with the use of a scanning electron microscope(SEM). Specifically, the pattern on a processed substrate is observedfrom above the substrate with use of the SEM, and an obtained SEM imageis binarized with the use of image editing software. In this manner, thediameters of the dots in the pattern are calculated to obtain thevariation coefficient.

Other than the SEM, the pattern shape can be evaluated with a planartransmission electron microscope (planar TEM), a cross-sectionaltransmission electron microscope (cross-sectional TEM), or the like. Thesame results as above can be achieved by measuring the shapes of thedots in the pattern by any of the above techniques, calculating thediameters of the dots, and obtaining a variation coefficient.

EXAMPLES

Hereinafter, examples are described.

Example 1

Referring now to FIGS. 1( a) through 1(e), a method of forming a finepattern according to Example 1 is described.

First, as shown in FIG. 1( a), a silicon substrate 2 was introduced intoa vacuum chamber of a sputtering device. The attainable degree of vacuumof the sputtering device was 1×10⁻⁵ Pa. A carbon film of 15 nm in filmthickness was formed as a hard mask 4 on the silicon substrate 2 (FIG.1( a)). The Ar pressure at the time of carbon film formation was 0.4 Pa,and the input power was 400 W.

The hard mask 4 comprised of the carbon film was formed on the siliconsubstrate 2, and a polydimethylsiloexane (PDMS) mask reinforcing member6 of 5 nm in thickness was formed on the hard mask 4 by the use ofspin-coating with a 0.05 wt % solution of (PDMS) using toluene as asolvent (FIG. 1( b)). A solution obtained by dissolving a di-blockcopolymer consisting of polystyrene (PS) having a molecular weight of11,700 and PDMS having a molecular weight of 2,900 in a propylene glycolmonomethyl ether acetate (PGMEA) solution was applied by a spin coatingtechnique, to form a di-block copolymer layer 8 of 22 nm in filmthickness (FIG. 1( c)). Annealing was then performed in a vacuum of 10Pa at 180° C. for 15 hours, to cause phase separations and form anordered array structure.

Convex portions were then formed as shown in FIG. 1( d). Specifically,reactive ion etching (RIE) was performed for 30 seconds, where theoxygen flow rate was 20 sccm, the total pressure was 0.1 Pa, the inputcoil power was 100 W, and the platen power was 10 W. Under suchconditions, etching was performed on a PS polymer layer 8 a, with thepolymer of a PDMS layer 8 b serving as a mask. Under the sameconditions, etching was performed on the PDMS layer 6 as the maskreinforcing member and the carbon hard mask 4, with the polymer 8 b andthe polymer 8 a serving as masks (FIG. 1( e)).

At this point, the upper face of the block copolymer layer 8 wasobserved with an atomic force microscope (AFM), to confirm that convexportions of approximately 10 nm in diameter, approximately 18 nm indepth, approximately 17 nm in pattern pitch were arranged in ahexagonal-lattice fashion.

The fine pattern formed under the above described conditions wasmeasured with a SEM, and the mean pattern size was estimated from anobtained SEM image. As a result, the diameter was approximately 13 nm,and the pattern pitch was approximately 17 nm. The pattern variation(the dot diameter variation) was measured from the SEM image, todetermine that the standard deviation was 1.1 nm. As a result, thevariation coefficient of the pattern shape of the carbon hard mask 4 offormed under the above described conditions was 8.5%.

COMPARATIVE EXAMPLE

As a comparative example of the above described Example 1, a pattern wastransferred and was measured through the same procedures as those ofExample 1, except that the mask reinforcing member 6 was not formed. Thesubstrate 2 after the transfer was measured with a SEM, and the meanpattern size was estimated, to determine that the diameter wasapproximately 13 nm, and the standard deviation was 3.4 nm. The resultsindicate that, where a pattern transfer was performed without the maskreinforcing member 6, the variation coefficient of the pattern was 24%.

FIGS. 2( b) and 2(c) are schematic views of the upper faces of patternstransferred onto the hard mask 4 with the use of the di-block copolymerlayer 8 having the ordered array structure shown in FIG. 2( a) by themethods according to the comparative example and Example 1,respectively.

As can be seen from FIG. 2( b), in the comparative example, theroughness of the edges of the dots is higher. In the case where the seaportions 8 a of the di-block copolymer layer 8 having a high etchingspeed are stacked directly on the hard mask 4, side etching is caused inthe di-block copolymer having a high etching speed at the interfacebetween the hard mask 4 and the di-block copolymer layer 8, and thepattern subjected to the side etching is transferred onto the hard mask4. As a result, the roughness of the edges of the dots becomes higher.In extreme cases, side etching is caused in the entire sea portions ofthe di-block copolymer layer 8, and the island portions cannot besupported, resulting in disappearance of the pattern.

By the method according to Example 1, on the other hand, the patternshape of the di-block copolymer layer 8 is accurately transferred ontothe hard mask 4, as can be seen from FIG. 2( c).

Example 2

Example 2 concerns the relationship between the film thickness of themask reinforcing member 6 and the variation coefficient of a transferredpattern, and the relationship between the film thickness of the maskreinforcing member 6 and the concavities and convexities of the hardmask.

A PDMS film was formed as the mask reinforcing member 6 on the 15-nmthick carbon hard mask 4 formed on each nonmagnetic glass substrate 2.Six samples were manufactured, with the thicknesses of the PDMS filmsbeing 0 nm, 2 nm, 5 nm, 10 nm, 15 nm, and 20 nm. It should be noted thatthe thickness of 0 nm means that the mask reinforcing member 6 is notformed. Under the same conditions as those in Example 1, a di-blockcopolymer layer was formed on each of the samples, and etching wasperformed. The RIE time was varied with the film thicknesses of the maskreinforcing members 6. The size variation (the variation coefficient) ofthe mask of each of the samples was determined from the results of sizemeasurement carried out with a SEM.

The patterns of the respective samples that were fabricated under theabove described conditions and had the mask reinforcing members 6 withdifferent film thicknesses were measured with the SEM to determine thevariation coefficients. The variation coefficient of the sample havingthe mask reinforcing member 6 of 0 nm in film thickness was 24%, thevariation coefficient of the sample having the mask reinforcing member 6of 2 nm in film thickness was 8%, the variation coefficient of thesample having the mask reinforcing member 6 of 5 nm in film thicknesswas 8%, and the variation coefficient of the sample having the maskreinforcing member 6 of 10 nm in film thickness was 9%. Meanwhile, thevariation coefficient of the sample having the mask reinforcing member 6of 15 nm in film thickness was 25%, and formation of a pattern was notseen in the sample having the mask reinforcing member 6 of 20 nm in filmthickness. The results of the measurement are shown in FIG. 3.

The diameter of each dot 8 b of the di-block copolymer (PS-PDMS) used inthis example is approximately 13 nm. Therefore, as can be seen from FIG.3, in the samples in which the film thicknesses of the PDMS films are 2nm, 5 nm, and 10 nm, which are equal to or smaller than the diameter,the values of the variation coefficients are smaller than the value ofthe variation coefficient of the sample not having the mask reinforcingmember 6. On the other hand, in the sample having the mask reinforcingmember 6 of 20 nm in film thickness, the PDMS layer 6 existing directlyon the hard mask 4 has a greater film thickness than the PDMS 8 bforming the pattern. Therefore, when etching is performed on the PDMSlayer serving as the mask reinforcing member 6, the PDMS 8 b forming thepattern in the di-block copolymer layer 8 disappears. As a result, thepattern in the di-block copolymer layer 8 cannot be transferred onto thehard mask 4.

FIG. 4 shows the relationship between the film thickness of the maskreinforcing member 6 and the concavities and convexities of the hardmask 4 on which a pattern is to be transferred. In the case whereetching is performed on the substrate 2, with the hard mask 4 serving asa mask, the hard mask 4 should preferably have a great film thickness.As can be seen from FIG. 4, once the film thickness of the maskreinforcing member 6 exceeds the radius of each dot 8 b of the di-blockcopolymer layer 8, the film thickness of the processed portion of thehard mask 4 becomes rapidly smaller. The result indicates that the filmthickness t of the mask reinforcing member 6 formed on the hard mask 4should preferably satisfy 0<t<d/2, where d represents the diameter ofeach dot 8 b of the mask.

Example 3

Referring back to FIGS. 1( a) through 1(e), a method of forming a finepattern according to Example 3 is described.

Samples were manufactured by forming a 5-nm thick mask reinforcingmember 6 by spin coating performed on the 15-nm thick carbon hard mask 4formed on each nonmagnetic glass substrate 2 (FIGS. 1( a) and 1(b)). Inthe respective samples, the mask reinforcing members 6 were apolyacrylic nitrile (PVN) film, a polyhydrostyrene (PHS) film, apolyvinylbiphenyl (PVB) film, a PS film, and a PDMS film. A di-blockcopolymer layer 8 was then formed on each of the samples under the sameconditions as those described in Example 1, and RIE was performed on themask reinforcing members 6 and the hard masks 4 (FIGS. 1( c) through1(e)). The RIE time was varied with the etching speeds for the maskreinforcing members 6. Where the etching speed for the PS was 1, theetching speeds of oxygen for the layers used as the mask reinforcingmembers 6 were 0.8 in the case of PVN, 1.0 in the case of PHS, 0.9 inthe case of PVB, 1 in the case of PS, and 0.5 in the case of PDMS. Atthis point, the etching speed for the carbon hard mask 4 was 0.3.

The patterns of the above samples were measured with a SEM to measurethe variation coefficients. As a result, the variation coefficients were9% in the case of PVN, 13% in the case of PHS, 12% in the case of PVB,13% in the case of PS, and 8% in the case of PDMS.

When a mask reinforcing member 6 was formed by mixing the abovepolymers, which were PVN, PHS, PVB, PS, and PDMS, a variationcoefficient of approximately 10% was obtained as in the cases wheresingle layers of the respective polymers were used.

Example 4

Referring again to FIGS. 1( a) through 1(e), a method of forming a finepattern according to Example 4 is described.

Samples were manufactured by forming a 5-nm thick mask reinforcingmember 6 by spin coating performed on the 15-nm thick carbon hard mask 4formed on each nonmagnetic glass substrate 2. In the respective samples,the mask reinforcing members 6 were a PS film, a PMMA(polymethylmethacrylate) film, and a PDMS film. Using PS-PMMA, adi-block copolymer layer 8 having a film thickness of 30 nm was thenformed on each of the mask reinforcing members 6 of the samples. Etchingwas then performed on the mask reinforcing members 6 and the hard masks4, and the patterns were transferred onto the hard masks 4.

Each PS-PMMA film was formed so that the proportion of the PMMA isapproximately 20%. After the film formation, a sea-island structurehaving islands formed by the PMMA can be obtained by annealing. In eachof the prepared samples, the pattern of the hard mask 4 after thepattern transfer was measured with a SEM to measure the variationcoefficient. The results indicated that the variation coefficient was15% in the case where a PS film was used as the mask reinforcing member6, 11% in the case of PMMA, and 18% in the case of PDMS.

Example 5

Referring again to FIGS. 1( a) through 1(e), a method of forming a finepattern according to Example 5 is described.

A 5-nm thick PDMS film as the mask reinforcing member 6 was formed byspin coating performed on the 15-nm thick carbon hard mask 4 formed on anonmagnetic glass substrate 2. A di-block copolymer (PS-PDMS) layer 8was then formed under the same conditions as those in Example 1, andetching was performed on the mask reinforcing member 6 and the hard mask4. The pattern was then transferred onto the hard mask 4. The pattern ofthe hard mask 4 after the transfer was measured with a SEM to measure avariation coefficient. The measurement result showed that the variationcoefficient was 8%.

Example 6

Referring now to FIGS. 5( a) through 6(c), a method of forming a finepattern according to Example 6 is described. The method of forming afine pattern according to Example 6 is used for forming a patternedmedium of a perpendicular magnetic recording type.

First, as shown in FIG. 5( a), a perpendicular magnetic recording layer3 was formed on a nonmagnetic glass substrate 2 with the use of asputtering device. In the perpendicular magnetic recording layer 3, asoft magnetic layer made of CoZrNb having a film thickness of 120 nm, anorientation control base layer having a film thickness of 20 nm, and aferromagnetic layer made of CoPt having a film thickness of 15 nm werestacked in this order. A hard mask 4 made of C (carbon) having a filmthickness of 15 nm was then formed on the perpendicular magneticrecording layer 3 with the use of a sputtering device.

A mask reinforcing member 6 and a di-block copolymer layer 8 made ofPS-PDMS were then formed under the same conditions as those in Example 1(FIGS. 5( b) and 5(c)). After that, RIE using O₂ was performed to formconcavities and convexities 8 a and 8 b in the di-block copolymer layer8 (FIG. 5( d)).

While the di-block copolymer layer 8 having the concavities andconvexities 8 a and 8 b was used as a mask, RIE using O₂ was performedon the hard mask 4, and the pattern was transferred onto the hard mask4, as shown in FIG. 6( a). At this point, the upper face of theperpendicular magnetic recording layer 3 was exposed through the bottomsof the concave portions of the transferred pattern.

While the pattern transferred onto the hard mask 4 is used as a mask,patterning was performed on the perpendicular magnetic recording layer 3exposed through the bottoms of the concave portions as shown in FIG. 6(b), with the use of an electron cyclotron resonance (ECR) ion gun and anAr gas, where the gas pressure was 0.04 Pa, the microwave power was 600W, the applied voltage was 600 V, and the processing time was 20seconds.

After that, ashing was performed for 20 seconds, where the oxygen flowrate was 20 sccm, the total pressure was 0.1 Pa, the input coil RF powerwas 200 W, and the platen RF power was 0 W. In this manner, the hardmask 4 remaining on the perpendicular magnetic recording layer 3 wasremoved, and a perpendicular magnetic recording medium was formed (FIG.6( c)).

The pattern in the CoPt ferromagnetic layer subjected to the patterningwas measured with a SEM, and the variation coefficient was measured. Themeasurement result showed that the variation coefficient was 12%. As isapparent from Example 1, the variation coefficient of the pattern in thehard mask 4 made of carbon is 8%. Through the etching later performed,however, the variation coefficient became higher than 8%.

COMPARATIVE EXAMPLE

As a comparative example of Example 6, a perpendicular magneticrecording medium was formed through the same procedures as those ofExample 1, except that the mask reinforcing member 6 was not formed. Thepattern in the CoPt ferromagnetic layer subjected to the patterning wasmeasured with a SEM, and the variation coefficient was measured. Themeasurement result showed that the variation coefficient was 33%.

By virtue of formation of a mark reinforcing member, a pattern can betransferred onto a magnetic recording layer without an increase in shaperoughness.

Example 7

Referring now to FIGS. 7( a) through 8(c), a method of forming a finepattern according to Example 7 is described.

First, a hard mask layer 4 made of C having a film thickness of 15 nmwas formed on a 6-inch Si substrate 2 (FIG. 7( a)).

Under the same conditions as those in Example 1, a mask reinforcingmember 6 and a di-block layer 8 made of PS-PDMS were successively formed(FIGS. 7( b) and 7(c)). A pattern having concavities and convexities 8 aand 8 b was then formed in the di-block layer 8 by RIE using O₂.

With the concavities and convexities 8 a and 8 b serving as a mask,etching was performed on the mask reinforcing member 6 and the hard mask4, and the pattern was transferred onto the hard mask 4 (FIG. 8( a)). Atthis point, the upper face of the Si substrate 2 was exposed through thebottoms of the concave portions of the transferred pattern.

While the hard mask 4 having the transferred pattern was used as a mask,45-second RIE was performed on the Si substrate 2 exposed through thebottoms of the concave portions, where the CF₄ gas flow rate was 20sccm, the total pressure was 0.1 Pa, the input coil RF power was 100 W,and the input platen RF power was 10 W. In this manner, the pattern ofthe ordered array structure 8 a and 8 b of the di-block copolymer layer8 was transferred onto the Si substrate 2 (FIG. 8( b)).

After that, ashing was performed for 20 seconds, where the oxygen flowrate was 20 sccm, the total pressure was 0.1 Pa, the input coil RF powerwas 200 W, and the platen RF power was 0 W. Through the ashing, the hardmask 4 remaining on the Si substrate 2 was removed, and the Si substrate2 having the pattern transferred thereonto was obtained (FIG. 8( c)).The pattern transferred onto the Si substrate 2 was measured with a SEM,and the variation coefficient was determined to be 13%.

Example 8

Referring now to FIGS. 9( a) through 9(e), a method of forming a finepattern according to Example 8 is described.

A 30-nm thick first hard mask 4 a made of C, a 3-nm thick second hardmask 4 b made of Si, and a 5-nm thick third hard mask 4 c made of C weresuccessively formed on a nonmagnetic glass substrate 2 with the use of asputtering device, to form a hard mask 4 having a structure in which thefirst hard mask 4 a, the second hard mask 4 b, and the third hard mask 4c were stacked (FIG. 9( a)).

Under the same conditions as those in Example 1, a mask reinforcingmember 6 and a di-block copolymer layer 8 made of PS-PDMS were formed(FIG. 9( b)). After that, etching with oxygen was performed on the maskreinforcing member 6 and the carbon of the third hard mask 4 c at thesame time as the etching of the PS portions 8 a of the di-blockcopolymer layer 8. In this manner, concavities and convexities wereformed in the carbon hard mask 4 c (FIG. 9( c)).

With the third hard mask 4 c serving as a mask, etching was performed onthe Si of the second hard mask 4 b (FIG. 9( d)). Specifically, where theCF₄ gas flow rate was 20 sccm, the total pressure was 0.1 Pa, the inputcoil RF power was 50 W, and the platen RF power was 10 W, RIE wasperformed on the Si of the second hard mask 4 b for 20 seconds.

After that, with the Si of the second hard mask 4 b serving as a mask,etching was performed on the carbon of the first hard mask 4 a.Specifically, where the O₂ gas flow rate was 20 sccm, the total pressurewas 0.1 Pa, the input coil RF power was 200 W, and the platen RF powerwas 10 W, RIE was performed on the C of the first hard mask 4 a for 40seconds, so that the pattern is transferred onto the first hard mask 4a. After that, the first hard mask 4 a having the pattern transferredthereonto serves as a mask, and etching was performed on the substrate2, so that the pattern was transferred onto the substrate 2 (not shown).

As the hard mask 4 has a three-layer structure, the film thickness ofthe first hard mask 4 a existing on the substrate 2 can be made greater.Accordingly, the mask durability can be made higher when the substrate 2is processed with the use of the mask.

On the other hand, as the hard mask 4 has the three-layer structure, thehard mask 4 is affected by side etching when the pattern is transferredfrom the carbon of the third hard mask 4 c onto the silicon of thesecond hard mask 4 b. As a result, the roughness in shape becomeshigher. Therefore, when the pattern transferred onto the substrate 2processed in the above described manner was measured with a SEM, aslightly high variation coefficient of 15% was obtained.

As described so far, according to this embodiment and each Example, anordered array pattern formed with a di-block copolymer can betransferred without an increase in pattern shape roughness. Accordingly,this embodiment and each Example can be applied to practical processingmethods for various products such as high-density recording media andhighly integrated electronic components, and a remarkable industrialadvantage can be gained.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel methods and systems describedherein can be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein can be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the inventions.

What is claimed is:
 1. A method of forming a fine pattern, the methodcomprising: forming a hard mask on a substrate; forming a maskreinforcing member on the hard mask; forming a di-block copolymer layeron the mask reinforcing member, the di-block copolymer layer comprisinga sea-island structure; forming a pattern comprising a concave-convexstructure in the di-block copolymer layer, with island portions of thesea-island structure being convex portions; and transferring the patternonto the hard mask by performing etching on the mask reinforcing memberand the hard mask, with a mask being the pattern formed in the di-blockcopolymer layer, wherein the mask reinforcing member is comprised of amaterial having an etching speed that is higher than an etching speedfor the hard mask and is lower than an etching speed for sea portions ofthe sea-island structure of the di-block copolymer layer.
 2. The methodaccording to claim 1, wherein the condition, 0<t<d, is satisfied, whered (nm) represents a diameter of each of the island portions forming thesea-island structure of the di-block copolymer layer, and t (nm)represents a film thickness of the mask reinforcing member.
 3. Themethod according to claim 1, wherein the mask reinforcing member iscomprised of one of or a combination of polyvinylnaphthalene (PVN),polyhydrostyrene (PHS), polyvinylbiphenyl (PVB), polystyrene (PS), andpolydimethylsilohexane (PDMS).
 4. The method according to claim 1,wherein a material of the island portions forming the sea-islandstructure of the di-block copolymer layer is the same as the material ofthe mask reinforcing member.
 5. The method according to claim 1, whereinthe di-block copolymer layer is comprised of a copolymer of polystyreneand polydimethylcyclohexane, and the mask reinforcing member iscomprised of polydimethylsilohexane.
 6. The method according to claim 1,further comprising transferring the pattern onto the substrate byperforming etching on the substrate with the use of the hard mask ontowhich the pattern is transferred.
 7. The method according to claim 1,wherein the hard mask comprises a structure in which a first hard maskcontaining carbon, a second hard mask containing silicon, and a thirdhard mask containing carbon are stacked in this order.
 8. The methodaccording to claim 1, wherein a ferromagnetic layer is formed on thesubstrate, and the method further comprises transferring the patternonto the ferromagnetic layer by performing etching on the ferromagneticlayer with the use of the hard mask onto which the pattern istransferred.
 9. The method according to claim 1, wherein the etching onthe mask reinforcing member and the hard mask is performed with the useof oxygen.